The headset comes with an item that is currently trading for 40 keys (1 key = ~$2). You could trade it away and get about $70-80 in Steam credit on the Steam Market, making the headset almost free (assuming you plan on buying more games off Steam eventually).

I would make sure the code is still valid and working in Dota2 before going this route.

*I suppose I should edit in that keys are used to open chests and are used at the base currency in Dota2 and TF2. Different keys are sometimes needed for different chests.